Catalyst system for producing aromatic carbonates

ABSTRACT

Hydroxyaromatic compounds such as phenol are carbonylated with oxygen and carbon monoxide in the presence of a catalyst system comprising a Group VIII metal having an atomic number of at least 44, preferably palladium; an alkali metal or alkaline earth metal halide, preferably sodium bromide; and at least one aliphatic polyether such as a polyethylene glycol dimethyl ether or a crown ether. The catalyst system also preferably contains a compound of another metal, preferably lead.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 09/383,425, filedAug. 27, 1999, now U.S. Pat. No. 6,114,564, entitled “CATALYSTCOMPOSITION AND METHOD FOR PRODUCING DIARYL CARBONATES” and,accordingly, claims priority to and the benefit of the filing date ofsaid application under 35 U.S.C. § 120. The parent application isincorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of diary carbonates bycarbonylation. More particularly, it relates to the improvement of diarycarbonate yield in the carbonylation reaction.

Diaryl carbonates are valuable intermediates for the preparation ofpolycarbonates by transesterification with bisphenols in the melt. Thismethod of polycarbonate preparation has environmental advantages overmethods which employ phosgene, a toxic gas, as a reagent andenvironmentally detrimental chlorinated aliphatic hydrocarbons such asmethylene chloride as solvents.

Various methods for the preparation of diaryl carbonates by an oxidativecarbonylation (hereinafter sometimes simply “carbonylation” for brevity)reaction of hydroxyaromatic compounds with carbon monoxide and oxygenhave been disclosed. In general, the carbonylation reaction requires arather complex catalyst. Reference is made, for example, to U.S. Pat.No. 4,187,242, in which the catalyst is a heavy Group VIII metal; i.e.,a Group VIII metal having an atomic number of at least 44, said metalsconsisting of ruthenium, rhodium, palladium, osmium, iridium andplatinum, or a complex thereof.

The production of carbonates may be improved by including a metal-basedcocatalyst along with the heavy Group VIII metal catalyst. Although theidentity of suitable metal-based cocatalysts will depend on specificreaction conditions including the identity of reactants and othermembers of the catalyst package, some general guidance can be found inU.S. Pat. Nos. 4,187,242 and 4,201,721.

A further development in the carbonylation reaction, including the useof specific lead compounds as cocatalysts, is disclosed in U.S. Pat. No.5,498,789. Also required according to that patent is the use ofquaternary ammonium or phosphonium halides, as illustrated bytetra-n-butylammonium bromide, as part of the catalyst package.Compounds characterized as inert solvents, such as toluene, diethylether, diphenyl ether and acetonitrile, can also be present.

The commercial viability of the carbonylation reaction would be greatlyincreased if a less expensive compound could be substituted for thequaternary ammonium or phosphonium halide. Substitution of suchcompounds as sodium bromide, however, result in the isolation of thedesired diaryl carbonate in low or insignificant yield.

It is of interest, therefore, to develop catalyst systems which includean inexpensive halide compound and which can efficiently produce diarylcarbonates. Some such systems are known. Reference is made, for example,to Japanese Kokai 10/316,627, which discloses the use of palladium and alead or manganese compound in combination with a halide such as sodiumbromide and with an amide or alkylurea. U.S. Pat. No. 5,726,340 andJapanese Kokai 9/278,716 disclose similar systems in which the lead iscombined with another metal and in which inert solvents such as thosementioned hereinabove may be present. The development of other systemsemploying relatively inexpensive halides, however, remains desirable.

SUMMARY OF THE INVENTION

The present invention provides a method for preparing diaryl carbonateswhich includes a relatively inexpensive halide and a compound whichmaximizes the effectiveness of said halide. Also provided are catalystcompositions useful in such a method.

In one of its aspects, the invention provides a method for preparing adiaryl carbonate which comprises contacting at least one hydroxyaromaticcompound with oxygen and carbon monoxide in the presence of an amounteffective for carbonylation of at least one catalytic materialcomprising:

(A) a Group VIII metal having an atomic number of at least 44 or acompound thereof,

(B) at least one alkali metal halide or alkaline earth metal halide, and

(C) at least one polyether.

Another aspect of the invention is catalyst compositions comprisingcomponents A, B and C as described above, and any reaction productsthereof.

DETAILED DESCRIPTION PREFERRED EMBODIMENTS

Any hydroxyaromatic compound may be employed in the present invention.Monohydroxyaromatic compounds, such as phenol, the cresols, the xylenolsand p-cumylphenol, are generally preferred with phenol being mostpreferred. The invention may, however, also be employed withdihydroxyaromatic compounds such as resorcinol, hydroquinone and2,2-bis(4-hydroxyphenyl)propane or “bisphenol A”, whereupon the productsare polycarbonate oligomers.

Other reagents in the method of this invention include oxygen and carbonmonoxide, which can react with the phenol to form the desired diarylcarbonate. They may be employed in high purity form or diluted withanother gas such as nitrogen, argon, carbon dioxide or hydrogen whichhas no negative effect on the reaction.

For the sake of brevity, the constituents of the catalyst system aredefined as “components” irrespective of whether a reaction between saidconstituents occurs before or during the carbonylation reaction. Thus,the catalyst system may include said components and any reactionproducts thereof.

Component A of the catalyst system is one of the heavy Group VIIImetals, preferably palladium, or a compound thereof. Thus, usefulpalladium materials include elemental palladium-containing entities suchas palladium black, palladium/carbon, palladium/alumina andpalladium/silica; palladium compounds such as palladium chloride,palladium bromide, palladium iodide, palladium sulfate, palladiumnitrate, palladium acetate and palladium 2,4-pentanedionate; andpalladium-containing complexes involving such compounds as carbonmonoxide, amines, nitrites, phosphines and olefins. Preferred in manyinstances are palladium(II) salts of organic acids, most often C₂₋₆aliphatic carboxylic acids, and palladium(II) salts of β-diketones.Palladium(II) acetate and palladium(II) 2,4-pentanedionate are generallymost preferred. Palladium(II) acetylacetonate is also a suitablepalladium source. Mixtures of the aforementioned palladium materials arealso contemplated.

Component B is at least one alkali metal or alkaline earth metal halide,preferably a bromide such as lithium bromide, sodium bromide, potassiumbromide, calcium bromide or magnesium bromide. Alkali metal bromides areespecially preferred, with sodium bromide often being most preferred byreason of its particular suitability and relatively low cost.

Component C is at least one polyether; i.e., at least one compoundcontaining two or more C—O—C linkages. The polyether is preferably freefrom hydroxy groups to maximize its desired activity and avoidcompetition with the hydroxyaromatic compound in the carbonylationreaction.

The polyether preferably contains two or more (O—C—C) units. Thepolyether may be “aliphatic” or mixed aliphatic-aromatic. As used in theidentification of the polyether, the term “aliphatic” refers to thestructures of hydrocarbon groups within the molecule, not to the overallstructure of the molecule. Thus, “aliphatic polyether” includesheterocyclic polyether molecules containing aliphatic groups withintheir molecular structure. Suitable aliphatic polyethers includediethylene glycol dimethyl ether (hereinafter “diglyme”), triethyleneglycol dimethyl ether (hereinafter “triglyme”), tetraethylene glycoldimethyl ether (hereinafter “tetraglyme”), polyethylene glycol dimethylether and crown ethers such as 15-crown-5(1,4,7,10,13-pentaoxacyclopentadecane) and 18-crown-6(1,4,7,10,13,16-hexaoxacyclooctadecane). Illustrative mixedaliphatic-aromatic polyethers are diethylene glycol diphenyl ether andbenzo-18-crown-6.

In a highly preferred embodiment of the invention, there is also presentin the catalyst system (D) at least one cocatalyst which is a compoundof a metal other than a heavy Group VIII metal. This metal is preferablyone which is soluble in the liquid phase under the reaction conditions.Numerous other metal compounds are known in the art to be active ascarbonylation cocatalysts, and any compound having such activity may beused according to the present invention provided an improvement indiphenyl carbonate production, usually yield, is achieved thereby.

Illustrative cocatalytic metals include cerium, titanium, cobalt,copper, zinc, manganese, iron and lead, which may be used singly or incombination. For the purposes of this invention the preferredcocatalysts are those containing metals other than Group VIII metals;that is other than iron, cobalt and nickel. More preferred are compoundsof lead, particularly when used alone or in combination with titaniumand/or cerium. It should be noted, however, that component C is noteffective to optimize diaryl carbonate formation for all possiblepermutations of component D; the combined effectiveness of the two forthis purpose may be determined by simple experimentation.

Examples of lead compounds which may be employed are lead oxides such asPbO and Pb₃O₄; inorganic lead salts such as lead(II) nitrate; leadcarboxylates such as lead(II) acetate and lead(II) propionate; leadalkoxides and aryloxides such as lead(II) methoxide and lead(II)phenoxide; and lead salts of β-diketones such as lead(II)2,4-pentanedionate. Mixtures of the aforementioned lead compounds mayalso be employed. The preferred lead compounds are lead(II) oxide,lead(II) aryloxides and lead(II) 2,4-pentanedionate.

Examples of cerium compounds are cerium carboxylates such as cerium(II)acetate, and cerium salts of β-diketones such as cerium(III)2,4-pentanedionate. Cerium(III) acetylacetonate and mixtures of theaforementioned cerium compounds may also be employed. The preferredcerium compounds are cerium 2,4-pentanedionates.

Examples of titanium compounds are inorganic titanium salts such astitanium(IV) bromide; titanium alkoxides and aryloxides such astitanium(IV) butoxide and titanium(IV) phenoxide; and titanium salts ofβ-diketones such as titanium(IV) oxide bis(2,4-pentanedionate).Titanium(IV) acetylacetonate and mixtures of the aforementioned titaniumcompounds may also be employed. The preferred titanium compounds aretitanium(IV) alkoxides, aryloxides and 2,4-pentanedionates.

The preferred compounds of other metals are, for the most part, salts ofβ-diketones and especially 2,4-pentanedionates.

In addition to the aforementioned reactants and catalyst system, it isstrongly preferred for a desiccant to be present in the reaction system.The preferred desiccants are non-reactive materials such as molecularsieves, as illustrated by 3-Ångstrom (hereinafter “3 Å”) molecularsieves. They are usually isolated from the other reactants, as bypresence in a basket mounted to a stirrer shaft or the like.

Component A is most often present in the amount of about 0.1-10,000 ppmby weight of the appropriate Group VIII metal (usually palladium), basedon the total of hydroxyaromatic compound and component C, and componentB in the amount of about 1-2,000 mol per mole of the Group VIII metal ofcomponent A. Component D, when employed, is generally present in theamount of about 1-200 mole of total metal per equivalent of the GroupVIII metal of component A.

The role of component C in the composition and method of the inventionis believed to be to increase the degree of dissociation and ionizationof the halide anion of component B, perhaps by forming a complex withthe cationic portion of said component, although the invention is in noway dependent on this or any other theory of operation. The amount ofcomponent C employed will be an amount effective to optimize diarylcarbonate formation, in general by increasing the yield of the desireddiaryl carbonate as evidenced, for example, by an increase in “turnovernumber”; i.e., the number of moles of diary carbonate formed pergram-atom of palladium present. This amount is most often about 1-60% byvolume based on the total of hydroxyaromatic compound and component C.

The amount of component C will, however, typically depend to some extenton the complexing ability of the organic compound employed. Crownethers, for example, have a very high complexing tendency with metalcations. For example, 15-crown-5 complexes efficiently with sodium and18-crown-6 with potassium. Such compounds may be used in amounts as lowas an equimolar amount based on component B. Other compounds useful ascomponent C, such as straight chain polyethers (e.g., diglyme), may beoptimally effective at much higher levels, often up to 1-60% by volumebased on total polyether and phenol; near the higher end of this range,they can also function as cosolvents. The preferred proportion of anyspecific material used as component C can be determined by simpleexperimentation.

The method of the invention is preferably conducted in a reactor inwhich the hydroxyaromatic compound and catalyst system are charged underpressure of carbon monoxide and oxygen and heated. The reaction pressureis most often within the range of about 1-500 and preferably about 1-150atm. Gas is usually supplied in proportions of about 1-50 mole percentoxygen with the balance being carbon monoxide, and in any event, outsidethe explosion range for safety reasons. The gases may be introducedseparately or as a mixture. Reaction temperatures in the range of about60-150° C. are typical. In order for the reaction to be as rapid aspossible, it is preferred to substantially maintain the total gaspressure and partial pressure of carbon monoxide and oxygen, asdescribed, for example, in U.S. Pat. No. 5,399,734, until conversion ofthe hydroxyaromatic compound is complete.

The diaryl carbonates produced by the method of the invention may beisolated by conventional techniques. It is often preferred to form andthermally crack an adduct of the diaryl carbonate with thehydroxyaromatic compound, as described in U.S. Pat. Nos. 5,239,106 and5,312,955.

The method of the invention is illustrated by the following examples.Minor variations in reagent amounts from one example to another are notbelieved significant from the standpoint of yield. Unless otherwisenoted, all equivalents are molar equivalents relative to palladium.

EXAMPLES 1-3

A constant composition gas flow reactor system, as disclosed in theaforementioned U.S. Pat. No. 5,399,734, was charged in each example with61.1 g (649 mmol) of phenol, 4.9 mg (0.016 mmol) of palladium(II)2,4-pentanedionate (28 ppm of palladium based on phenol), 205 mg (0.92mmol, 58 eq.) of lead(II) oxide, 650 equivalents of sodium bromide orlithium bromide and various proportions of 15-crown-5 or diglyme.Molecular sieves, 38 g, were placed in a perforatedpolytetrafluoroethylene basket mounted to the stir shaft of the reactor.

The reactor was sealed, pressurized to 89.8 atm with a mixture of 9.1mole percent oxygen and 90.9 mole percent carbon monoxide and stirred asits temperature was increased to 100° C. over 10 minutes. Furtheroxygen-carbon monoxide mixture was introduced at a flow rate of 330ml/min and a pressure of about 88.5 atm. Gas flow was continued for 2.5hours, during which the reaction mixture was analyzed every 30 minutesby high pressure liquid chromatography.

The results are given in Table I, in comparison with two controls:Control 1 in which the bromide source was tetraethylammonium bromide(TEAB), and Control 2 in which sodium bromide was employed without theuse of component C. Turnover numbers are those observed at the point ofhighest diphenyl carbonate content of each reaction mixture, as shown byanalysis.

TABLE I Component Component Component Turnover Example B C identity Cvol. % number 1 NaBr 15-Crown-5 3.5 5,455 2 NaBr Diglyme 54 1,655 3 LiBrDiglyme 10.8 2,212 Control 1 TEAB — — 5,587 Control 2 NaBr — —   626

It can be seen that the proportion of diphenyl carbonate produced, asshown by turnover number, is substantially higher for Examples 1-3 thanfor Control 2 in which component C was not employed. In Example 1, theturnover number was comparable to that of Control 1 employing theconsiderably more expensive quaternary ammonium bromide.

EXAMPLE 4

The procedure of Examples 1-3 was repeated except that the molecularsieves were omitted, the polyether was tetraglyme at 7.9% by volume andthe levels of palladium, lead and sodium bromide were 17 ppm, 56gram-atoms and 357 equivalents, respectively. The turnover number was2,857.

EXAMPLE 5

The procedure of Examples 1-3 was repeated except that the polyether wastetraglyme at 26% by volume, the bromide was potassium bromide at alevel of 775 equivalents and the level of lead was 56 gram-atoms. Theturnover number was 4,128.

EXAMPLES 6-8

A Parr 450-ml Hastelloy reactor was charged at room temperature withphenol (80-85 g), Pd(II) 2,4-pentanedionate (component A) at variouslevels, 56 eq. lead(II) oxide, 4 eq. titanium(IV) oxide2,4-pentanedionate, polyether (4.5-8.5% by volume) and sodium bromide atvarious levels. Molecular sieves (3 Å, 30 g) were placed in a perforatedpolytetrafluoroethylene basket mounted to the stir shaft of the reactor.The reactor was sealed and pressurized to 108.8 atm with a mixture of 9%(by volume) oxygen and 91% carbon monoxide. The reactor was heated understirring (1600 rpm) to 100° C. over 10 min and stirred over 1.5 hours,with periodic sampling. Tetraglyme or a polyethylene glycol dimethylether having a molecular weight of about 250 (designated “PEGDME”) wasemployed as component C. The results are given in Table II.

TABLE II Example 6 7 8 Component A, 17 13 14 ppm Component B, 230 448454 eq Component C Tetraglyme Tetraglyme PEGDME vol. % (8.45) (7.15)(4.77) Turnover 4,620 6,.145 6,784 number

EXAMPLES 9-16

Carbonylation experiments were conducted in small vials, employingpalladium(II) 2,4-pentanedionate (24 ppm of palladium based on phenoland cosolvent), sodium bromide and various ethers. Various cocatalystcompounds which included lead(II) oxide, titanium(IV) oxidebis(2,4-pentanedionate), cerium(III) 2,4-pentanedionate and copper(II)2,4-pentanedionate, employed alone or in combination, were employed ascomponent D. Each vial was capped with snap caps having a slit with apolytetrafluoroethylene septum and the vials were placed in an autoclavewhich was pressurized to 81.6 atm with a mixture of 91.7 mole percentcarbon monoxide and 8.3 mole percent oxygen and heated at 100° C. for 3hours. The contents of the vials were analyzed for diphenyl carbonate byvapor phase chromatography.

The results are given in Table III as averages of duplicate ortriplicate runs. Cocatalyst proportions are in equivalents perequivalent of palladium, and ether proportions are in percent by volumebased on phenol. Controls contain an equivalent volume of phenol insteadof component C.

TABLE III Control Exam- Component Component Component Turnover turnoverple B, eq C (vol. %) D metal (eq) number number 9 445 PEGDME Pb (48)2,804 215 (15) 10 270 Triglyme Pb (48) 1,186 152 (35) 11 111 PEGDME Pb(47), Ti 1,481 162 (15) (10) 12 270 Triglyme Pb (47), TI 1,249 472 (35)(10) 13 106 Diglyme Pb (47), Ce 1,065 183 (15) (6) 14 100 PEGDME Pb(47), Ce 1,098 183 (15) (6) 15 111 PEGDME Cu (20) 941 218 (15) 16 111PEGDME Cu (20), 1,233 160 (15) Ti (10)

What is claimed is:
 1. A catalyst composition comprising the following:(A) a Group VIII metal having an atomic number of at least 44 or acompound thereof, (B) at least one alkali metal halide or alkaline earthmetal halide, and (C) at least one polyether, wherein the polyether ofcomponent C increases the degree of dissociation and ionization of thehalide anion of component B.
 2. A composition according to claim 1further comprising (D) at least one cocatalyst which is a compound of ametal which is not a Group VIII metal having an atomic number of atleast
 44. 3. A composition according to claim 2 wherein component C isan aliphatic polyether free from hydroxy groups.
 4. A compositionaccording to claim 2 wherein component A is palladium(II) acetate orpalladium(II) 2,4-pentanedionate.
 5. A composition according to claim 2wherein component D is lead(II) oxide, a lead(II) aryloxide or lead(II)2,4-pentanedionate.
 6. A composition according to claim 2 whereincomponent D is at least one member selected from the group consisting oflead(II) oxide, a lead(II) aryloxide, and lead(II) 2,4-pentanedionate,wherein the lead compound is combined with at least one member selectedfrom the group consisting of titanium(IV) alkoxide, titanium(IV)aryloxide, and titanium(IV) 2,4-pentanedionate.
 7. A compositionaccording to claim 2 wherein component D is at least one member selectedfrom the group consisting of lead(II) oxide, a lead(II) aryloxide, andlead(II) 2,4-pentanedionate, wherein the lead compound is combined witha cerium 2,4-pentanedionate.
 8. A composition according to claim 2wherein component B is sodium bromide.
 9. A composition according toclaim 2 wherein component C is selected from the group consisting ofdiethylene glycol dimethyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, polyethylene glycol dimethyl ether,15-crown-5 and 1 8-crown-6.
 10. A composition according to claim 9wherein component C is diethylene glycol dimethyl ether, triethyleneglycol dimethyl ether or tetraethylene glycol dimethyl ether.
 11. Acatalyst composition comprising the following: (A) a Group VIII metalhaving an atomic number of at least 44 or a compound thereof, (B) atleast one alkali metal halide or alkaline earth metal halide, (C) atleast one polyether, and (D) copper(II) bis(2,4-pentanedionate), whereinthe polyether of component C increases the degree of dissociation andionization of the halide anion of component B.
 12. A catalystcomposition comprising: (A) palladium or a compound thereof, (B) sodiumbromide, (C) at least one aliphatic polyether free from hydroxy groups,and (D) at least one lead compound.